Reading devices of the above referred to type and particularly reading devices which are portable and may be placed upon a desk comprise a projection screen in the shape of a plate having a frosted surface on one side. With devices as now known, such plate is vertically or approximately vertically mounted to present to an observer a screen picture which is as uniformly illuminated as possible. However, with an optical system of the kind here involved, the projection assembly producing light rays impinge upon the side of the screen opposite to the frosted side and are dispersed at the level of the frosted side thereof. Accordingly, if the screen and the vertical side thereof is substantially vertically disposed the largest light component in the dispersed light rays impinges upon the eyes of the observer but from the margin of the projected picture, depending upon the observation angle, only the deflected light ray components reaches the eyes of the observer. As a result, the projection as seen by the observer on the screen appears at its margin and is considerably darkened.
To handle the reading device in a convenient manner, the microfilm or fiche is disposed below the screen plate. Accordingly, observation of the picture as appearing on the screen requires continuous stiff and vertical holding of the head of the observer. Such stiff holding of the head is obviously tiring or even painful, especially if the observer wants to make written notes on the table upon which the reading device is placed. Such written notes are often required due to the nature of the information obtained from viewing the screen. Working under such conditions is made even more inconvenient if as is usually the case with reading devices as now known are rather voluminous and occupy most of the table.
Due to the afore pointed out disadvantages of reading devices in which the light rays are directed upon the rear side of the projection screen reading devices are also used to provide impingement of the light rays upon the upper side of a horizontally disposed screen. However, reading devices of this type have the disadvantage that the observer can view the screen only at an angle. Moreover, due to the placement of the mirror system above the screen the device is bound to be very bulky and the mirrors tend to become dusty rather soon thereby reducing the clarity of the projection.
As is apparent, both types of now known reading devices as hereinbefore described have advantages and disadvantages.